1. Field of the Invention
This invention relates to a process for making copolymers of maleic anhydride and an alkyl vinyl ether, and, particularly, to a solution feed, slurry polymerization process for making high viscosity copolymers within a predetermined viscosity range.
2. Description of the Prior Art
Several methods are known for preparing copolymers of maleic anhydride (MA) and an alkyl vinyl ether, e.g. methyl vinyl ether (MVE). For example, it is known:
(1) To react a charge of MA dissolved in a large excess of MVE in a pressure reactor. However, this method is disadvantageous because considerable heat is evolved during the polymerization, and, under these process conditions, it is difficult to remove this heat effectively. Furthermore, homopolymers of MVE can form during the polymerization, and this by-product reduces the overall viscosity of the product obtained.
(2) To control the heat released during the reaction, molten MA has been fed into a reactor precharged with a large excess of MVE. Unfortunately, in this method, the reaction rate is strongly dependent upon the degree of agitation provided in the reactor, which parameter is difficult to regulate. As a result, the viscosity of the copolymers obtained cannot be controlled effectively.
(3) Another available method requires feeding molten MA into a reactor precharged with MA dissolved in a solvent. This method avoids the necessity of a large excess of MVE; however, as in method (2) above, it is very difficult to monitor the feed rate of molten MA into the reactor, and, accordingly, localized polymerization occurs with the resultant formation of undesirable by-products.
(4) MVE also can be fed into a reactor precharged with MA dissolved in a solvent. However, this method does not provide high viscosity copolymers within a predetermined viscosity range.